1. Field of the Invention
The present invention relates to a pan-tilt unit for positioning or aiming a device, such as a camera.
2. Description of Related Art
Pan-tilt units are used to position, aim, steer or otherwise orient a device in a desired direction by moving the device about two perpendicular axes. One common application is the field of surveillance and security where a camera is mounted to a pan-tilt unit that can be controlled or programmed to scan a desired area. Another application involving cameras is the field of videoconferencing where a video camera is mounted to a pan-tilt unit that can be controlled from a remote location to direct a camera toward a particular individual in a room.
Pan-tilt movement is conventionally accomplished using separate motors that independently perform the pan and tilt operations. For example, a pan-tilt unit generally includes a pan motor for rotating the device about a pan axis, and a tilt motor for rotating the device about a tilt axis that is perpendicular to the pan axis.
In known pan-tilt units, at least one of the drive motors is typically mounted to a structure that is rotated about one of the axes by the other motor. For example, the tilt motor in many pan-tilt units is mounted to a portion of the unit that is rotated about the pan axis by the pan motor as described in U.S. Pat. No. 5,463,432 to Kahn. In such configurations, the pan motor must be capable of delivering sufficient power to move the mass of the tilt motor and its accompanying drive mechanism. Consequently, the unit may require a pan motor that is larger than would otherwise be necessary if it did not have to physically move the mass of the tilt motor. The use of larger motors leads to a relatively heavier unit that consumes a higher amount of power to perform the panning and/or tilting operations.
An example of a proposed pan-tilt unit that attaches the drive motors to a stationary housing is described in U.S. Pat. No. 4,945,459 to Ferren et al. A two-axis beam steering system for use in automated light fixtures is configured so that the drive motors are not bodily moved during the steering operations of the unit. Rotational movement of the light beam is achieved using separate drive mechanisms that include multiple pulleys and belts that couple the pulleys to the drive motors.
It is an object of the present invention to provide an improved pan-tilt unit.